<!DOCTYPE html>
<html lang="zh_CN">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script type="text/javascript">
    var str = 'abca';
    var newStr = str.replace('a', 'A');
    console.log(newStr, str);
</script>

</html>
